1. Field of Invention
The present invention relates to mounting devices and techniques for sensitive components or parts. The invention is more particularly related to the mounting or attachment of an Liquid Crystal on Silicon (LCOS) microdisplay directly to a surface of a prism assembly. The invention also features a structure that allows the LCoS or other mounted component to be demounted from the prism assembly should it be necessary for reasons such as repair, inspection, etc., and other mounting and mating features that minimize the build up of thermally and/or mechanically induced stress near and in the microdisplay.
2. Discussion of Background
Light Engines are utilized in optical devices, particularly projection video devices and generally comprises a light source, condenser, kernel, projection lens, and a display screen, and related electronics. The function of the components of an LCoS based video projector 100 is explained with reference to FIG. 1. As shown, white light 110 is generated by a light source 105. The light is collected, homogenized and formed into the proper shape by a condenser 115. UV and IR components are eliminated by filters (e.g., hot/cold mirrors 116/117). The white light 110 then enters a prism assembly 150 where it is polarized and broken into red, green and blue polarized light beams. A set of reflective microdisplays 152A, 152B, and 152C are provided and positioned to correspond to each of the polarized light beams (the prism assembly 150 with the attached microdisplays is called a kernel). The beams then follow different paths within the prism assembly 150 such that each beam is directed to a specific reflective microdisplay. The microdisplay that interacts with (reflects) the green beam displays the green content of a full color video image. The reflected green beam then contains the green content of the full color video image. Similarly for the blue and red microdisplays. On a pixel by pixel basis, the microdisplays modulate and then reflect the colored light beams. The prism assembly 150 then recombines the modulated beams into a modulated white light beam 160 that contains the full color video image. The resultant modulated white light beam 160 then exits the prism assembly 150 and enters a projection lens 165. Finally, the image-containing beam (white light beam 160 has been modulated and now contains the full color image) is projected onto a screen 170.
Many different prism assemblies are commercially available in many varying configurations. However, the kernel is generally the optical heart of the light engine. The kernel is composed of the prism assembly and three LCOS microdisplays. Establishing the physical/spatial relationship between the microdisplays and the prism assembly is an important aspect of light engine design and production.
The current state of the art in establishing a physical relationship between the microdisplays and the prism assembly utilizes an air gap between the surfaces of the prism assembly and the upper surfaces of the microdisplays. FIG. 2 is an illustration of a conventional six-axis mounting system for alignment of microdisplays on a prism assembly. As illustrated in FIG. 2, the physical relationship of the microdisplays is established by mounting each microdisplay on an individual six-axis adjustment stage. The assembly process requires a procedure for mutually aligning the microdisplays to an accuracy that is typically on the order of +/xe2x88x922 microns. There are several unfavorable consequences that follow as a result of adopting this mounting approach:
The cost of each light engine includes the considerable expense of three, six-axis positioners.
After initial set up, it is unlikely that the three microdisplays will remain within the required alignment tolerance during subsequent assembly process, steps and during product transport.
An additional expense is incurred with the application anti-reflection (AR) coatings to the front surfaces of the three microdisplays and the three facing surfaces of the prism.
The AR coated surfaces are exposed to dust, moisture and atmospheric contaminates and are therefore likely to deteriorate with time which will result in a degraded projected image.
A solution to the above stated problems is to mount and optically couple the microdisplays directly to the surfaces of the prism. Direct mounting reduces the cost by at least the price of the 3 six-axis adjustment stages, requires no post production alignment or other adjustments because the microdisplays are fixed in position, and eliminates or reduces the need for anti-reflection coatings. However, despite the considerable advantages that could be derived by doing so, few companies currently build kernels in this configuration. One reason is the difficulty in reworking defective products. That is, a defective directly mounted microdisplay is difficult to remove from an otherwise good prism assembly. Conversely, good microdisplays are difficult to remove from a defective prism.
In addition, direct mounting of microdisplays causes other problems, including the build up of stress as the temperature of the light engine increases during operation. The origin of the stress is the difference in the coefficient of thermal expansion that exists between the materials in the prism and in the microdisplay. Consequences of stress include:
Birefringence in the prism and cover glass of the microdisplay. The birefringence can cause distortion in the projected image; and
Physical distortion of the microdisplay. Such distortion induces fringing that will be visible in the projected image.
The present inventors have realized the need to provide a device or method for direct mounting of microdisplays in a manner that allows for easy removal. The invention described herein allows the microdisplay to be mounted directly to the surfaces of the prism such that the microdisplay can be de-mounted should the need arise. And, the present invention includes procedures and techniques to bond the microdisplay to the prism in such a way as to minimize the build up of stress.
The present invention is embodied as an optical device, comprising, an optical component, a microdisplay mounted to the optical component with an adhesive, and a guide mounted in relation to the optical component and the microdisplay such that insertion of a dislodging tool in the guide results in an increased probability that the dislodging tool strikes the adhesive bond between the microdisplay and prism.
In another embodiment, the present invention is a microdisplay package, comprising, a carrier having a mounting surface capable of affixing to a non-optical surface of a microdisplay, and a bezel extending from the carrier in a direction of an optical surface of the microdisplay, wherein, when said microdisplay is fixed to a device surface with an adhesive layer, the bezel acts as a guide for a dislodging tool to impact the adhesive layer.
In another embodiment, the present invention is a device package, comprising, a carrier comprising a substantially planar platform having a mounting area suitable for affixing to a non-optical surface of a microdisplay, and a bezel extending from the carrier toward a plane defined by an optical surface of the microdisplay when the microdisplay is affixed to the mounting area at the non-optical surface.
In yet another embodiment, the present invention is a device package, comprising, a device, a carrier comprising a substantially planar platform affixed to a non-optical surface of the device, and a bezel extending from the carrier toward a plane defined by an optical surface of the device.
Ultimately, the present invention is preferably suited for use in a light engine of a projection television, computer monitor, or other display device. Therefore, the present invention may also be embodied as a projection television, comprising, a screen, a prism assembly including a microdisplay fitted into a package, said package comprising a carrier having a substantially planar platform affixed to a first surface of the microdisplay, a bezel extending from the carrier toward a plane defined by a second surface of the microdisplay opposite the first surface, a light engine coupled to said prism assembly, and a lens configured to focus light emitted from said prism assembly onto the screen.
Thus, the present invention provides the best advantages of both a direct mounting technique (e.g., fixed registration, low mounting cost), and an adjustable axis mounting technique (easy removal for maintenance/replacement, low/no stress build-up between microdisplay and prism).